This invention generally relates to an apparatus for producing ribbed, spiral seamed pipes, particularly pipes made from 30 gauge steel or thinner with multiple ribs between the seams.
Spiral seamed pipes made from strips of sheet metal are widely used to transport fluids. For example, these pipes are frequently used to transport air to ventilate, heat or cool buildings. In this application, as well as others, it is desired that the pipe produced is strong, lightweight and inexpensive, and provides minimal resistance to fluid flow. The pipe must be sufficiently strong to maintain rigidity over long expanses and against pressure from external forces. Any aberration in the uniformity of the inner pipe surface, such as a bend or dent, increases the resistance to fluid flow through the pipe. It is desirable for the pipe to be lightweight so that less manpower is required to carry and install it. Two ways to reduce weight are to use a lighter metal and less of it. The type and amount of metal also affects the cost of the pipe and usually its strength.
One approach to strengthing a spiral pipe is shown in U.S. Pat. No. 3,132,616 to Hale et al. This patent discloses an apparatus which is intended to form fluid-tight spiral pipes from band stock. This patent teaches the formation of two open-channel corrugation grooves in the band stock which serve to stiffen the pipes. The grooves are formed as the band stock passes between two pairs of forming rollers before being shaped into a pipe. Each pair of rollers comprises a lower roller with two annular ribs protruding from its surface and a corresponding upper roller with two annular grooves formed in its surface, each rib fitting into a corresponding groove. As the band passes between the first set of rollers, the ribs and grooves cooperate to form two longitudinal, parallel, open-channel grooves of a first diameter in the band. The second pair of rollers makes the grooves deeper and narrower as its ribs are higher and grooves are deeper.
While these open-channel grooves improve the rigidity of the pipe, they also have some shortcomings. They create turbulence within the fluid flowing along the walls of the pipe. This turbulence results in higher friction loss and noise in the fluid flow.
Finnish Patent Application No. 344/71 to OY NOKIA AB, which was laid open to inspection in 1980, discloses an alternate approach to strengthening pipes made from a lighter metal (typically 24-26 gauge). The machine disclosed in this reference produces a spiral seamed pipe with a single, loop-shaped ridge between the seams. This ridge is produced by three pairs of rollers which form an open-channel groove in the middle of the band and a fourth set of rollers which pinches the sides of the groove together at its base to form the hollow ridge. The ridge stiffens the pipe more than an open-channel groove so that lighter metals can be used to make a pipe. In addition, closing the base of the ridge makes the inner surface of the pipe smoother, thereby reducing frictional resistance to fluid flow through the pipe.
Notwithstanding these advantages, the pipes produced by the Finnish Machine also have certain drawbacks. Conventional thinking dictates that the higher the ridge the greater the strength. In applications requiring strong pipes, a high ridge would be employed. However, in some applications it has been found that the top of the ridge folds over and collapses before the full strength of the ridge is utilized. Thus, the material that comprises the top of the ridge adds relatively little additional strength to the pipe. This problem is exacerbated with lighter metals (e.g. thinner than 26 gauge). In addition, these pipes are flexible over long expenses as the ridges tend to separate at their bases. Another drawback is that, fluid is able to penetrate and move within the ridge cavity at multiple points along the length of the pipe. This causes a whistling sound as the fluid travels through this ridge. Also, where the pipe is cut off, the ends of these ridges are open, thereby allowing the fluid in the ridges to escape from the system. If this penetration is to be positively prevented, the base of the ridges must be sealed (e.g., by welding) as well as the open ends of the ridges where the pipe is cut off.
The present invention responds to the drawbacks and limitations of the prior art by providing an improvement in a spiral pipe producing apparatus for producing triple ribbed, spiral seamed pipe. The apparatus includes at least three pairs of corrugation rollers. A first pair of corrugation rollers has a center rib and two outer ribs which cooperate with a center groove and two outer grooves for forming three parallel corrugation grooves in the metal strip. A second pair of corrugation rollers has a center rib and two outer ribs which cooperate with a center groove and two outer grooves for forming the corrugation grooves in the metal strip deeper and narrower. The outer ribs and outer grooves of the second corrugation roller pair are inwardly displaced relative to the outer ribs and outer grooves of the first corrugation roller pair. A third pair of corrugation rollers has a center rib and two outer ribs which cooperate with a center groove and two outer grooves for forming the corrugation grooves in the metal strip deeper and narrower. The outer ribs and outer grooves of the third corrugation roller pair are inwardly displaced relative to the outer ribs and outer grooves of the second corrugation roller pair. Squeezer means then squeeze together the sides of the corrugation grooves to produce three parallel ribs in the metal strip.
In the preferred embodiment, two or more ribs are formed between the seams. Also, no more than ten pairs of rollers or squeezers are mounted in the apparatus so that pipes of different metal gauges and rib configurations can be made on the same machine by merely interchanging the various rollers and squeezers. The preferred embodiment employs only two edge forming roller assembly pairs to bend the outer edges of the strip into a conventional configuration that is capable of producing a very tight lockseam. The first pair of rollers bends the left edge of the strip downwardly at an angle less than 45.degree. and the right-edge into a V-shaped channel. The second roller pair further bends the left edge downwardly so that it is perpendicular to the strip, and bends the outer edge of the V-shaped channel upwardly so that it is perpendicular with respect to the strip. Five pairs of corrugation rollers are used to form the grooves progressively deeper and narrower.
In the present invention, the rollers and squeezers cooperate to produce a ribbed pipe that overcomes many of the disadvantages associated with pipes produced by prior art machines. First, the present invention can produce spiral pipes from 30 gauge metal or lighter (e.g. 33 gauge) that is as strong, or stronger, than pipes produced from conventional machines and provides low resistance to fluid flow. The thinner gauge metal weighs and costs less than the materials that are commonly used in conventional machines. The plurality of closed ribs between the seams provides greater strength, and the strength increases as the number of ribs increases. In fact, it is very difficult to make spiral pipe from 33 gauge metal without the ribs of this invention because the metal strip is so weak that it tends to collapse in the forming head. The multiple rib configuration also provides greater strength with less material since the ribs do not have to be as high. Moreover, the smaller rib height permits the pipes to fit within smaller spaces, and may provide a more pleasing aesthetic effect. Another advantage is that the ribs are preferably squeezed together (as opposed to hollow) so that fluid does not travel within the ribs. Thus, the ends of the ribs do not have to be sealed when the end of the pipe is cut off. All these advantages can be realized using one machine which accommodates 10 or fewer pairs of various combinations of rollers and squeezers.
These and other advantages of the present invention will be apparent from the following description of the preferred embodiment, annexed drawings, and appended claims.